We are originally from the Seattle area and visit Washington regularly, we are going to spend a week in Depoe Bay on the Oregon Coast in August. Although I love the Oregon Coast, I don't know if I'd recommend going all that distance for two nights. Even 3 or 4 nights would be iffy for us, for that distance. Typically for us to drive from Tacoma, about 45 minutes south of Seattle (on a good traffic day - the traffic is awful), to the very beginning of the Oregon Coast - Astoria - would be around 5 hours. To go further to areas like Cannon Beach or Lincoln City, it's going to be around 8 hours, particularly in June when Highway 101 can slow to a crawl on some days. So, I think that's the first thing you have to figure out - do you want to spend that much time traveling? You could take the Amtrak or fly to Portland, but you would still need to rent a car to get to the coast and it would still be a couple of hours of driving.
If you do want to go to the southern Washington Coast, that can be driven to in maybe 3 hours. And they are similar in geographical makeup. There is Ocean Shores, with lots of hotels and a beautiful open beach. If you want something more secluded, we rented a nice house from
www.pacificbeachandbeyond.com in a remote, less developed area on the pacific side of the Olympic Mountains. They rent for 2 nights.
Parking is a problem in Seattle, but some hotels do include parking. If you just want to stay in Seattle it can be done via public trans and walking, but to see most things outside of Seattle you'll need a car.
Another option is to taken the ferry to the San Juans and stay for a couple of nights - they are gorgeous and actually very close to Seattle. There are lots of beaches, artists, farms, parks and places to hike. LaConner or Anacortes are also good option for a weekend, very cute, B&B sort of towns on the coast - they are on the coast too but they are protected by the islands, so it's a different feel than the southern Wa or Oregon coast that are more open to the Pacific's power. Or visit the cascades if you enjoy the mountains and hiking. Too many things to really pick one, but that's probably the best plan for a couple of days.
Have a wonderful time, we are hoping to do a cruise to Alaska next summer for our 20th anniversary! If you can get more than a couple of days to visit Washington or Oregon, I'd really recommend it. It's a great place to visit, but because it's a large state it takes some travel time to get places.